U.S. patent number 5,970,433 [Application Number 08/799,484] was granted by the patent office on 1999-10-19 for laser obstacle detection method and sensor.
This patent grant is currently assigned to Mitsui Engineering & Shipbuilding Co. Ltd.. Invention is credited to Masujiro Hisatani, Hiroshi Imajo, Koji Oka, Toru Takehara.
United States Patent |
5,970,433 |
Oka , et al. |
October 19, 1999 |
Laser obstacle detection method and sensor
Abstract
A sensor detects the presence or the absence of an obstacle by
radiating a laser beam to the outside of a casing through a light
projecting mirror and by letting the reflected light from an
obstacle enter a light receiving element through a light receiving
mirror. A light projecting window with a light projecting mirror
positioned and a light receiving window with a light receiving
mirror are positioned in the casing with a space therebetween to
prevent reflected light from directly entering the light projecting
window. The mirrors are attached to a rotation shaft of a motor, or
rotation shafts of motors, synchronously rotatable provided between
both mirrors. The optical axis of light radiated to the outside of
the casing is set to face in a higher direction than horizontal to
radiate in a cone-shaped form. By comparing a received light signal
from a light receiving circuit to an output signal from a circuit
for a previously set threshold, which has a correlation between
detected distance and light intensity, a light receiving trigger is
output. The distance is calculated when a signal is greater than
the threshold. The presence or the absence of an obstacle is
determined by the detection of reflected light intensity. This
laser obstacle detection method and sensor, which can be used on an
automated guided vehicle (AGV), will not misdetect rainfall as an
obstacle.
Inventors: |
Oka; Koji (Tamano,
JP), Hisatani; Masujiro (Tamano, JP),
Imajo; Hiroshi (Tamano, JP), Takehara; Toru
(Tamano, JP) |
Assignee: |
Mitsui Engineering &
Shipbuilding Co. Ltd. (Tokyo, JP)
|
Family
ID: |
16124916 |
Appl.
No.: |
08/799,484 |
Filed: |
February 12, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Jun 24, 1996 [JP] |
|
|
8-182814 |
|
Current U.S.
Class: |
702/159;
250/559.13; 356/4.07; 702/150; 250/559.39; 702/40; 398/151 |
Current CPC
Class: |
G01S
7/4811 (20130101); G01S 17/931 (20200101); G02B
26/105 (20130101); G05D 1/024 (20130101); G01S
7/4817 (20130101); G05D 1/0272 (20130101); G01S
7/4873 (20130101); G01S 7/4816 (20130101) |
Current International
Class: |
G05D
1/02 (20060101); G02B 26/10 (20060101); G01S
17/00 (20060101); G01S 17/93 (20060101); G01S
7/481 (20060101); G01C 003/00 () |
Field of
Search: |
;364/525,526,805,556,551.01,561,580,604 ;701/28,96,211,301
;340/901,903,904,937,942,435,436,437,433 ;342/69,70,54
;356/4.01,4.07,5.01,152.3,4.04,375,380,386,387,5.03 ;180/167,169
;359/205,208,221,154,155,561,731,857,861,864,869
;250/559.38,559.39,559.13,559.26,234-236 ;372/15,24 ;235/467
;702/40,94,97,134,135,136,143,150,159,158,172 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
A-0 269 902 |
|
Jun 1988 |
|
EP |
|
A-3-177905 |
|
Aug 1991 |
|
JP |
|
A-4-27331 |
|
Jan 1992 |
|
JP |
|
A-4-67641 |
|
Mar 1992 |
|
JP |
|
A-2-161 340 |
|
Jan 1986 |
|
GB |
|
A-2 274 368 |
|
Jul 1994 |
|
GB |
|
A-2 290 918 |
|
Jan 1996 |
|
GB |
|
Primary Examiner: Wachsman; Hal Dodge
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A laser obstacle detection method that uses a sensor disposed in
a casing for detecting the presence or the absence of an obstacle
outside of the casing by radiating a laser light beam from a light
source to the outside of the casing and when a potential obstacle
is present receiving light reflected from the potential obstacle to
a light receiving element disposed in the casing, the method
comprising the steps of:
determining a threshold light intensity signal based on a
correlation of detected distance and light intensity;
radiating a laser light beam outward from the casing and generating
a light projecting signal;
receiving a light beam reflected back to the light receiving
element and generating a light receiving signal;
comparing the generated light receiving signal to the threshold
light intensity signal;
calculating and outputting a distance detected to a potential
obstacle based on the generated light receiving signal and the
light projecting signal when the reflected light beam has an
intensity greater than the threshold light intensity signal;
and
determining whether the potential obstacle is an obstacle based on
a relationship between the detected distance and a relative
direction of the sensor to the potential obstacle.
2. The laser obstacle detection method of claim 1 wherein the step
of radiating a laser light beam outward from the casing includes
reflecting the laser beam with a light projecting mirror.
3. The laser obstacle detection method of claim 1 wherein the step
of receiving a light beam reflected back to the light receiving
element includes using a light receiving mirror disposed in the
casing.
4. The laser obstacle detection method of claim 1 wherein the step
of determining a threshold light intensity signal based on a
correlation of detected distance and light intensity includes
establishing a plurality of predetermined threshold values based on
intensity of the light beam reflected to the light receiving
element and distance, resulting in a generally hyperbolic
relationship.
5. A laser obstacle detection sensor assembly for detecting
presence of an obstacle using light radiated from a light source
and reflected back from a potential obstacle, comprising:
a casing from which light is radiated therefrom, the casing having
a central driving section;
a light projecting window formed in the casing;
a light projecting mirror disposed in the casing facing the light
projecting window;
a light receiving window formed in the casing, the light receiving
window being spaced from the light projecting window, wherein the
central driving section is located between the light projecting
window and the light receiving window and extends outwardly from
the light projecting window and light receiving window thus forming
an eave that prevents raindrops from directly contacting the light
projecting window;
a light receiving mirror disposed in the casing facing the light
receiving window to prevent light directly reflected from the light
projecting window from entering the light receiving window; and
a drive source housed in the central driving section and coupled to
the light projecting mirror and the light receiving mirror that
drives the light projecting mirror and the light receiving mirror
in synchronous rotation.
6. The laser obstacle detection sensor assembly of claim 5 wherein
the drive source comprises a single motor with a rotation shaft
that supports the light receiving mirror and the light projecting
mirror.
7. The laser obstacle detection sensor assembly of claim 5 wherein
the drive source comprises motors having drive shafts that are
synchronously rotatable and that support the light receiving mirror
and the light projecting mirror.
8. The laser obstacle detection sensor assembly of claim 5 wherein
the light projecting window and the light receiving window are
annular and provide 360 degree radiation and receipt of light.
9. The laser obstacle detection sensor assembly of claim 5 wherein
the light projecting mirror has a reflecting surface with an
optical axis that is disposed in a direction higher than horizontal
and light is reflected from the reflecting surface in a cone-shaped
form.
10. A laser obstacle detection sensor assembly for detecting
presence of an obstacle using light radiated from a light source
and reflected back from a potential obstacle, comprising:
a casing from which light is radiated therefrom;
a light projecting window formed in the casing;
a light projecting mirror disposed in the casing facing the light
protecting window;
a light receiving window formed in the casing, the light receiving
window being spaced from the light projecting window;
a light receiving mirror disposed in the casing facing the light
receiving window to prevent light directly reflected from the light
projecting window from entering the light receiving window; and
a drive source coupled to the light protecting mirror and the light
receiving mirror that drives the light projecting mirror and the
light receiving mirror in synchronous rotation,
wherein the light receiving mirror has a reflecting surface
including a flat reflecting portion and a curved reflecting portion
having varied curvature.
11. A laser obstacle detection sensor for detecting presence of an
obstacle based on a light radiated from the sensor and reflected
back to the sensor, comprising:
a light receiving element that receives a light signal reflected
back from a potential obstacle;
a light receiving circuit connected to the light receiving element
that converts the received light signal into a photoelectric signal
representative of reflected light intensity;
a threshold setting circuit that generates a preset threshold
output signal based on a correlation between a distance from an
obstacle and light intensity; and
a determiner coupled to the threshold setting circuit and the light
receiving circuit that compares the photoelectric signal of
reflected light intensity to the preset threshold output signal
and, when the photoelectric signal of reflected light intensity is
greater than the threshold output signal, determines the presence
of the obstacle.
12. The laser obstacle detection sensor of claim 11, wherein the
determiner also determines a distance to the obstacle.
13. The laser obstacle detection sensor of claim 11 wherein the
threshold setting circuit sets a plurality of predetermined
threshold values based on intensity of light beam reflected to the
light receiving element and distance, resulting in a generally
hyperbolic relationship.
14. A laser obstacle detection sensor assembly for detecting
presence of an obstacle using light radiated from a light source
and reflected back from a potential obstacle, comprising:
a casing from which light is radiated therefrom;
a light projecting window formed in the casing;
a light projecting mirror disposed in the casing facing the light
projecting window;
a light receiving window formed in the casing, the light receiving
window being spaced from the light projecting window;
a light receiving mirror disposed in the casing facing the light
receiving window to prevent light directly reflected from the light
projecting window from entering the light receiving window;
a drive source coupled to the light projecting mirror and the light
receiving mirror that drives the light projecting mirror and the
light receiving mirror in synchronous rotation;
a light receiving element coupled to the light receiving mirror
that receives a light signal from light reflected back from the
potential obstacle;
a light receiving circuit connected to the light receiving element
that converts the received light signal into a photoelectric signal
representative of reflected light intensity;
a threshold setting circuit that generates a preset threshold
output signal based on a correlation between a distance from an
obstacle and light intensity; and
a determiner coupled to the threshold setting circuit and the light
receiving circuit that compares the photoelectric signal of
reflected light intensity to the preset threshold output signal
and, when the photoelectric signal of reflected light intensity is
greater than the threshold output signal, determines the presence
of the obstacle.
15. The laser obstacle detection sensor assembly of claim 14
wherein the light projecting mirror has a reflecting surface with
an optical axis that is disposed in a direction higher than
horizontal and light is reflected from the reflection surface in a
cone-shaped form.
16. The laser obstacle detection sensor assembly of claim 15
wherein the light receiving mirror has a reflecting surface
including a flat reflecting portion and a curved reflecting portion
having varied curvature.
17. A laser obstacle detection sensor assembly that detects the
presence of an obstacle, comprising:
a laser light source that radiates a laser light beam;
a light projecting mirror that reflects the laser light beam toward
a potential obstacle;
a light receiving element that receives light reflected back from
the potential obstacle; and
a light receiving mirror that reflects light from the potential
obstacle to the light receiving element, wherein the light
receiving mirror has a reflecting surface including a flat
reflecting surface and raised elongate reflecting surface generally
centrally disposed on the flat reflecting surface, the raised
reflecting surface having a curved projecting portion.
18. The laser obstacle detection sensor assembly of claim 17,
wherein the raised reflecting surface has a generally T-shape.
19. The laser obstacle detection sensor assembly of claim 17,
wherein the curved projecting portion has more than one radius of
curvature.
20. The laser obstacle detection sensor assembly of claim 17,
wherein the curved projecting portion flares upwardly to a
projecting point.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a laser obstacle detection method
and sensor, and particularly to a laser obstacle detection method
and sensor which can effectively prevent misdetection of an object
which is not essentially an obstacle, such as raindrops, snowfall,
or the like, as an obstacle, when equipped on a vehicle for
detecting an obstacle in a traveling area.
Generally, an electromagnetic induction automated guided vehicle
automatically traveling on a specified traveling road along an
induction line by detecting an induction signal outputted from an
induction line previously laid on the road surface (Japanese Patent
Application Publication No. 4-67641), and an automatic driving
system for vehicles driving a guided vehicle based on an amount of
relative displacement between a white line laid on a road and the
guided vehicle which is detected by a CCD camera (Japanese Patent
Application Laid-open No. 4-27331) are known to be used as an
automatic driving system of an automated guided vehicle.
Since laying an induction line on the entire traveling reference
line is restricted by cost and has many inconveniences, such as
trouble of a broken line and so on caused by vehicles and so on
traveling on the induction line, a system is proposed which travels
and is induced by bodies as detecting signs consisting of magnets
which are embedded at specified intervals on the traveling
reference line (Japanese Patent Application Laid-open No.
3-177905). A traveling route in which a magnet is embedded with a
specified interval provided is formed and a sensor for calculating
displacement by detecting magnetism of each magnet is attached on a
vehicle body. An azimuth sensor is provided on the vehicle body,
and by calculating the deviation from azimuth information
previously set between adjacent magnets, the vehicle automatically
travels along the route to its goal.
Incidentally, for an automatically traveling automated guided
vehicle, when moving along the traveling route prescribed in the
above, it is important to take a measure such as an automatic halt
and so on when the existence of an obstacle is recognized on a
traveling route, and to this end, an obstacle detection sensor is
provided. As sensors of this kind, a method for radiating a
ultrasonic wave and a method for radiating a millimeter wave are
conventionally known, however they have disadvantages of low
responsiveness resulting in detecting an obstacle at only one point
and being unable to detect human beings, of low sensitivity in
rainfall and snowfall, and of catching noise and so on. Therefore,
recently there has been a tendency to use an obstacle detection
sensor using a laser beam for reasons of having high resolution at
a long distance with high directivity and surely detecting human
beings. Such a laser sensor radiates a laser beam projected from
the light source in a side direction of the vehicle, then detects
the reflected light from an obstacle in the range of a traveling
route and calculates the distance to determine when to halt the
vehicle and so on in accordance with the extent of the distance to
the obstacle. The conventional laser obstacle detection sensors are
provided with a light sending and receiving window at the casing
for projecting a laser beam from the window to the outside through
a light projecting mirror, and for detecting the reflected light
from the same window through a half mirror. The reflected light is
input to a photoelectric element, and the time from the radiation
to the reception of the reflected light is calculated to calculate
the distance. In order that precipitation such as raindrops are not
detected as an obstacle, a method for detecting reflected light
intensity is adopted, and generally only a signal with a reflection
intensity greater than a specified threshold is detected as an
obstacle.
However, in the conventional laser obstacle detection sensor, there
is a disadvantage of being unable to surely prevent misdetection of
raindrops as a ghost obstacle at rainfall, though a method for
detecting an obstacle only when reflected light with intensity more
than a specified level is detected especially from a viewpoint that
reflected light intensity from raindrops is small. On the window
forming the laser beam projecting portion and receiving portion, a
light transmittable protective plate such as acrylic resin or the
like is attached and there are disadvantages of detecting the
vehicle itself equipped with the sensor being detected as an
obstacle and of mistakenly recognizing reflected light from
contacting water drops which are directly received when raindrops
and so on contact this protective plate. Further, in an automated
guided vehicle or the like requiring a sensor of this kind, the
inclination of a vehicle body caused by partial loading, or the
detection of the ground surface as an obstacle due to the vibration
during traveling occur, and these things empirically occur
especially in rainfalls.
SUMMARY OF THE INVENTION
Mitigating the above-described conventional disadvantages, an
object of the present invention is to provide a laser obstacle
detection method and sensor which are especially effective to be
equipped on an automated guided vehicle (AGV) and which do not
misdetect raindrops and so on as an obstacle. The second object of
the present invention is to provide a laser obstacle detection
method and sensor which can prevent the misdetection of raindrops
in contact with the laser beam projecting and receiving windows.
Further, the third object of the present invention is to provide a
laser obstacle detection method and sensor which can prevent the
misdetection of a ground surface on which a vehicle is traveling as
an obstacle.
The present invention relates to a sensor for detecting the
presence or the absence of an obstacle by radiating laser beam
radiated from a laser beam source to the outside of a casing
through the medium of a light projecting mirror and by letting the
reflected light from an obstacle or the like enter a light
receiving element through the medium of a light receiving mirror
and particularly to a sensor. A light projecting window with a
light projecting mirror positioned so as to face the light
projecting window and a light receiving window with a light
receiving mirror positioned so as to face the light receiving
window are formed, with a space provided between, in the casing to
prevent reflected light directly from the light projecting window
from being received. The above-described mirrors are attached to a
rotation shaft of the same motor or rotation shafts of motors
synchronously rotatable which is, or are, provided between both the
mirrors to enable synchronized rotation of the light projecting
mirror and the light receiving mirror. An optical axis of light
radiated to the outside of the casing through the medium of a
reflecting surface of said light projecting mirror is set to face
in a higher direction than the horizontal line to radiate
projecting laser beam as a rotating laser beam in a cone-shaped
form. By comparing a received light signal from a light receiving
circuit to an output signal from a circuit for a previously set
threshold having a correlation between detected distance and light
intensity, a light receiving trigger is outputted and the distance
is calculated when a signal is greater than the threshold. The
presence or the absence of an obstacle is determined by the
detection of reflected light intensity with the above-described
threshold as a boundary. Thereby the present invention is
especially effective when equipped on an automated guided vehicle
(AGV) wherein the laser obstacle detection method and sensor do not
misdetect rainfall or the like as an obstacle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of the laser obstacle detection sensor
relating to the embodiment;
FIG. 2 is a side view showing an external appearance of the same
sensor;
FIGS. 3 (A) to 3 (C) are explanatory views of a sensor detecting
range as a result of the inclination of an automated guided vehicle
and an explanatory view of a light projecting mirror, and FIG. 3
(A) shows a detecting condition of the conventional sensor, while
FIG. 3 (B) shows a detecting condition of the present embodiment
and FIG. 3 (C) is a side view of the light projecting mirror;
FIG. 4 (A) is a front view of the light receiving mirror, and FIG.
4 (B) is a side view of the light receiving mirror, while FIG. 4
(C) is an explanatory view of a light receiving condition;
FIG. 5 is a block diagram of the sensor; and
FIG. 6 is an explanatory diagram of the threshold of light
intensity.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The laser obstacle detection method relating to the present
invention, which is an obstacle detection method using a sensor for
detecting the presence or the absence of an obstacle by radiating a
laser beam radiated from a laser beam source to the outside of a
casing through the medium of a light projecting mirror and by
letting the reflected light from an obstacle or the like enter a
light receiving element through the medium of a light receiving
mirror, consists of the steps of comparing a received light signal
inputted to the above-described light receiving element to a
threshold previously determined by the correlation between a
detected distance and light intensity, calculating and outputting
the detected distance up to an obstacle or the like based on the
received light signal and a light projecting signal when a
reflected light with intensity greater than the threshold is
detected, and determining the presence or the absence of the
obstacle.
The laser obstacle detection sensor related to the present
invention is a sensor for detecting the presence or the absence of
an obstacle by radiating a laser beam radiated from a laser beam
source to the outside of a casing through the medium of a light
projecting mirror and by letting the reflected light from an
obstacle or the like enter a light receiving element through the
medium of a light receiving mirror. The assembly includes a light
projecting window and a light receiving window being formed with a
space provided between in the above-described casing, with the
light projecting mirror being positioned so as to face the
above-described light projecting window and with the light
receiving mirror being positioned so as to face the above-described
light receiving window. So, reflected light directly entering from
the above-described light projecting window is prevented from being
received. Both of the above-described mirrors are attached to a
rotation shaft of a motor provided between both the mirrors, so
that the light projection mirror and the light receiving mirror can
be synchronously rotated.
In this case, an optical axis of the light radiated to the outside
of the casing through the medium of the reflecting surface of the
above-described light projecting mirror is set in a higher
direction than the horizontal line. Thereby, a laser projected
light can be radiated as the laser projection light is rotated in a
cone-shaped form.
The sensor according to the invention is characterized by a
received light reflecting surface of the above-described light
receiving mirror. The reflecting surface is constructed by a
combined reflecting surface reflecting light to the above-described
light receiving element and having a flat reflecting portion and a
curved reflecting surface with varied curvatures.
Further, the sensor according to the invention is characterized by
including a light receiving circuit for conducting photoelectric
conversion of the received light signal from the above-described
light receiving element. Also provided is a threshold setting
circuit for precisely setting the threshold by the correlation
between the detected distance and the light intensity, and a
calculating section for comparing reflection light intensity output
from the above-described light receiving circuit to a threshold
output signal at the light receiving time from the above-described
threshold setting circuit and for outputting the detected distance
up to an obstacle when the reflected light intensity output is
greater than the threshold output at the light receiving time. So,
the presence or absence of an obstacle is determined by the
detection of the reflected light intensity with the above-described
threshold as a boundary.
More specifically, the present invention has a construction
characterized by the light projecting window and the light
receiving window being formed with a space provided therebetween in
the above-described casing, with the light projecting mirror being
positioned so as to face the above-described light projecting
window and with the light receiving mirror being positioned so as
to face the above-described light receiving window. So, reflected
light directly from the above-described light projecting window is
prevented from being received. Both of the above-described mirrors
are attached to a rotation shaft of the same motor provided between
both the mirrors, so that the light projecting mirror and the light
receiving mirror can be synchronously rotated. An optical axis of
the light radiated to the outside of the casing through the medium
of the reflecting surface of the above-described light projecting
mirror is set in a direction higher than the horizontal line, and
radiated laser projection light is rotated in a cone-shaped form.
The received light reflecting surface of the above-described light
receiving mirror is constructed by a combined reflecting surface
reflecting light to the above-described light receiving element and
has a flat reflecting portion and a curved reflecting surface with
varied curvatures. The invention includes a light receiving circuit
for conducting photoelectric conversion of the received light
signal from the above-described light receiving element, a
threshold setting circuit for previously setting the threshold by
the correlation between the detected distance and the light
intensity, and a calculating section for comparing the reflected
light intensity output from the above-described light receiving
circuit and for outputting the detected distance up to an obstacle
when the reflection light intensity output is greater than the
threshold output at the light receiving time. So, the presence or
absence of an obstacle is determined by detection of the reflected
light intensity with the above-described threshold as a
boundary.
By the above-described construction, in which the threshold level
varying in accordance with a distance is set for the laser
reflection light intensity output, misdetection of raindrops or the
like caused by rainfall or snowfall as an obstacle is prevented.
Specifically, the present invention is made by noticing the fact
that the intensity of reflected or reflection light is varied
depending on the position of reflecting raindrops at rainfall
though the entire level of the intensity of reflected light is low
when a radiated laser beam is reflected by raindrops or the like.
The invention is also designed from the viewpoint that the
reflection light intensity from raindrops at a close distance is
sufficiently large while the reflection light intensity decreases
as a distance becomes longer. The threshold of the reflection light
intensity is set large in case of a short distance, and the
threshold is set smaller as the detected distance becomes longer,
so that an obstacle is detected when the light intensity is greater
than this threshold and raindrops are detected when the light
intensity is smaller than the threshold. Therefore, misdetection of
raindrops as an obstacle can be prevented. By constructing the
assembly so as to separate the light projecting section and the
light receiving section up and down, misdetection of a vehicle body
and so on as an obstacle, which can occur as a result of picking up
the reflection from contacting raindrops, and the reflection light
from attaching water directly entering the light receiving mirror
can be prevented. These problems occur to the conventional sensor
with the light projecting section and the light receiving section
provided at the same position. Further, the light receiving mirror
is a combined reflecting surface with varied curvatures, so that
detection of an obstacle at a short distance is easy and an
obstacle in close proximity can be surely detected while
misdetection caused by raindrops at a short distance is especially
prevented by increasing a detection range. In addition, since the
optical axis of the light projected from the projection mirror is
set to face in a higher direction than the horizontal line, a
ground surface is prevented from being detected as an obstacle when
a vehicle is tilted.
A preferable embodiment of the laser obstacle detection method and
sensor relating to the present invention will be particularly
described below with reference to the drawings.
FIG. 1 illustrates construction of a laser obstacle detection
sensor 10, and FIG. 2 illustrates an external view thereof. As
illustrated in the drawings, the sensor 10 includes equipment
within a cylindrical casing 12, and is defined by a driving section
casing 12D incorporating rotary driving equipment, a light emitting
section casing 12L connected to the bottom thereof through the
medium of a light projecting chamber 14, and a light receiving
casing 12R connected to the top thereof through the medium of a
light receiving chamber 16, all of which are formed to be
concentric cylinder forms.
As a laser beam source, a semiconductor laser oscillator 18 is
used. Being positioned within the light emitting section casing 12L
at the lower part of the casing, the semiconductor laser oscillator
18 enables the radiation of laser beam in an upward direction of
the center line of the casing toward the inside of the light
projecting chamber 14. At a central position of the casing inside
the light projecting chamber 14, a light projecting mirror 20 is
positioned, and this light projecting mirror 20 reflects the laser
beam radiated from the laser oscillator 18 to project the light
toward the outside of the casing 12 from a light projecting window
14W forming the side wall of the light projecting chamber 14. The
light projecting window 14W is formed of a transparent acrylic
plate in an annular from, and is constructed so as to be able to
project light outwards from the entire surface around the
circumference. In this case, the diameter of the light projecting
window 14W is set to be smaller than the diameter of the casing 12
so that a portion of the bottom surface of the driving section
casing 12D forms so-called eaves at the top of the light projecting
window 14W to prevent raindrops from directly contacting the light
projecting window 14W.
Inside the driving section casing 12D positioned on the top of the
above-described light projecting chamber 14, attached is a DC motor
22, which has rotating shafts concentric with the central axis of
the casing at both ends. At one rotating shaft facing downward of
this DC motor 22, the light projecting mirror 20 is attached with
the foremost end facing the above-described light projecting room
14. Accordingly, the light projecting mirror 20 can rotate 360
degrees by the rotation of the motor 22, and can project laser
emission light outwardly from the above-described light projecting
window 14W formed to be annular as a rotating laser beam.
An encoder 24 is attached on the other rotating shaft facing upward
of the DC motor 22, and the foremost end of the rotating shaft
faces the above-described light receiving chamber 16 through a
coupling 26, a shaft bearing 28 and so on further on the encoder
24. At the rotating shaft projecting inside this light receiving
chamber 16, a light receiving mirror 30 is attached. This light
receiving mirror 30, which is positioned in the area of the central
axis of the casing, receives the laser beam entering through the
light receiving window 16W forming the side wall of the light
receiving chamber 16, and reflects the laser beam in an upward
direction along the central axis of the casing so that the laser
beam enters the light receiving section casing 12R on the top. Like
the light projecting window 14W, this light receiving window 16W is
formed of a transparent acrylic plate in an annular form, and is
constructed so as to receive laser beams from the outside on the
entire surface around the circumference. The diameter of the light
receiving window 16W is set to be small like the above-described
light projecting window 14W so that the external surface of the
window is positioned inside the casing 12 and a portion of the
bottom of the light receiving section casing 12R functions as eaves
to prevent raindrops from contacting the surface of the window.
Though the light projecting mirror 20 and the light receiving
mirror 30 are rotatable by the DC motor 22 as described above, the
light projecting direction from the light projecting mirror 20 and
the light receiving direction of the light receiving mirror 30 are
naturally set to face the same direction seen from the horizontal
surface. Even in a rotating condition of 360 degrees by the
rotating drive of the motor 22, the light projecting and light
receiving directions are set to be synchronized so that when the
projected laser beam is reflected from an obstacle and so on, the
light receiving mirror 30 can receive the reflected light. Thereby
the detection of an obstacle in the area of 360 degrees around the
casing 12 is possible. The above-described light projecting window
14W and the light receiving window 16W are separated up and down by
the central driving section casing 12D, and the driving section
casing 12D on the middle stage prevents the laser beam projected
from the light projecting mirror 20 from directly radiating to the
light receiving mirror 30, or the light receiving window 16W when
the projected laser beam short-cuts.
The reflected light from the light receiving mirror 30 is directed
to the central lower surface of the light receiving section casing
12R on the top, and there a honey-comb filter 32 is positioned so
that a light receiving circuit 36 receives the light through the
medium of a light receiving section optical system 34 such as a
condenser and so on. The light receiving circuit 36 is equipped
with a photoelectric conversion element 38 so as to convert
received light into an electric signal and obtain a received light
signal.
As seen in FIG. 3B, this sensor 10 can be equipped on an automated
guided vehicle 40, and it is possible that the vehicle 40 is in a
partial loading condition depending on a loaded position of a
carried load and that one side of the vehicle 40 is tilted down. In
such a condition, it is possible that the sensor 10 detects a
ground surface as an obstacle, therefore in this embodiment, as
illustrated in FIGS. 3 (A) to 3 (C), a reflecting direction of the
light projecting mirror 20 is not set to be orthogonal to the
central axis of the casing, but the optical axis of the reflection
light of the light projecting mirror 20 is set to face higher than
the horizontal line. Thereby when the light projecting mirror 20 is
rotated by the motor 22, the projecting laser beam is radiated as
it is rotating in a cone-shaped form. Specifically, as FIG. 3 (A)
illustrates, when the heavy-weighted side of the vehicle 40 is
tilted down at partial loading, the sensor casing 12 secured on the
vehicle 40 is also tilted down. Therefore when the laser beam is
projected in the direction perpendicular to the shaft core of the
casing, the reflection from the ground surface ahead of the vehicle
40 at distance L.sub.S is detected and misdetected as an obstacle.
Therefore, as FIG. 3 (B) illustrates, a laser beam projecting
outside the casing is set to face an upward direction, so that the
distance in which the radiated laser beam reaches the ground
surface is set to be a long distance L.sub.L on the heavyweighted
side. Specifically, as FIG. 3 (C) illustrates, this can be achieved
by setting the inclination of the reflection surface of the light
projecting mirror 20 to the shaft core of the casing 12 to be in
the angle range of 44.degree.<.theta.<45.degree., preferably
set at 44.5.degree.<.theta.<44.7.degree., and by setting the
projecting angle of the mirror reflection light to be an upward
angle with an inclination of below 1.degree. to the horizontal
surface, while ordinarily, the reflection surface of the light
projecting mirror 20 has an inclination of 45.degree. to the shaft
core of the casing 12. In the embodiment, one of the two sensors 10
set at the right and left areas on the front end of the vehicle 40
is set at 44.7.degree., and the other is set at 44.5.degree., and
by signals from both sensors 10, the presence or the absence of the
reflection from the ground surface is detected.
FIGS. 4 (A) to 4 (C) illustrate the details of the light receiving
mirror 30 receiving the reflected laser light entering from the
outside of the casing 12. As FIG. 1 also illustrates, this light
receiving mirror 30 has a combined reflection surface having a
planar reflection portion with the reflection surface being set to
be a slope of 45.degree. and a curved reflection surface with the
curvature of the reflection surface being varied in order that
light enters the photoelectric conversion element 38 positioned on
the shaft core of the casing 12. Specifically, the light receiving
mirror 30 has a raised planar portion being in a reverse T-shaped
form in a central portion of a first reflection surface 30L formed
to be a polygonal planar surface. At the lower part of this raised
portion, a second reflection surface 30M with a small rectangular
area for reflection in a medium range is formed, while a third
reflection surface 30S for a short range is slenderly raised in a
curved upward direction from this second reflection surface 30M.
With the raised height being increased from the above-described
second reflection surface 30M to the third reflection surface 30S,
the raised height is formed by a curve of a secondary degree or a
curve of a multiple degree which is set so that the reflected light
at each reflection point is parallel to each other. In other words,
the focus is farther than the setting position of the honey-comb
filter 32 in order that the reflected light at each position on the
surface passes through the honey-comb filter 32 defining the light
receiving section optical system. When the light reflecting from an
obstacle in close proximity enters the light receiving mirror 30, a
reflection curved surface can be empirically formed by adjusting a
curvature at each reflection point according to a approximate
distance in order that the mirror reflection angle can be directed
to the honey-comb filter 32. Thereby, the second reflection surface
30M is set to have a gradually increasing tangent inclination angle
at a reflection point compared to the first reflection surface 30L,
and the third reflection surface 30S is further set to have a
further gradually increasing tangent inclination angle at a
reflection point. As a result, as FIG. 4 (C) illustrates, in the
case of sole use of the first reflection surface 30L, the light
reflecting from an obstacle close to the vehicle 40 is deviated
from the light receiving range when the light reflects from the
mirror surface (a broken line in the drawing), but the light can be
received by the second or the third reflection surface 30M or 30S
(a solid line in the drawing).
The light receiving circuit 36 inputting a received light signal is
incorporated in the light receiving section casing 12R, and this
circuit detects at least a light intensity signal by conducting
photoelectric conversion of the received light signal. This output
signal of this light receiving circuit 36 is compared to an output
signal from a threshold setting circuit having a correlation
between a detected distance (time) and light intensity, and when
the received light signal is greater than the threshold, a received
light trigger is generated to measure the time from light
projecting to light receiving and then to calculate the distance. A
preferred construction is illustrated in FIG. 5.
As illustrated in the drawing, when the light receiving circuit 36
receives the reflection light, the signal as a result of the
photoelectric conversion of the reflection light is inputted in a
comparator 42. The comparator 42 compares a comparison standard
signal to a received light signal, and the standard signal takes in
an output signal from a threshold setting circuit 44. That is to
say, the comparator 42 compares a set standard light intensity to a
received light signal and determines that the received light is
caused by rainfall or snowfall and not by an obstacle when
receiving the light with the intensity below the standard light
intensity, and the standard light intensity is discriminated with a
standard signal taken in from the threshold setting circuit as a
threshold. This threshold signal is selected especially for
excluding the reflected light from raindrops, and the present
invention prevents the misdetection of the ghost signal of the
raindrops appearing at a short distance as an obstacle by setting a
threshold excluding the raindrops as a function of the distance
based on the knowledge that the light intensity of the raindrop
reflection signal fluctuates according to a distance. That is to
say, as FIG. 6 illustrates, when the intensity of the reflected
light (/.circle-solid. raindrops signal) in the case of the
raindrops reflecting light being detected and the intensity of the
reflected light (obstacle signal .backslash..largecircle.) in the
case of an obstacle being detected are obtained by artificially
creating a raining condition and by changing the distance between
the position of the raindrops and the sensor 10, there appears a
tendency closely analogous to a hyperbola function in which at a
short distance, the intensity of the reflected light from the
raindrops is strong, and in which as the distance is longer, the
intensity of the light is reduced. Then, in the threshold setting
circuit 44, the threshold regarding the distance is set as a
hyperbola function along the raindrops detection range (a solid
line in FIG. 6). Alternatively, FIG. 6 can be represented as a
table, and likewise, is set as the threshold regarding the
distance. The output of this threshold setting circuit 44 is
inputted in the comparator 42, and the threshold corresponding to
the received light signal output which is to be compared fluctuates
according to the distance from the object from which the light
reflects. Therefore, a corresponding threshold becomes a comparison
standard signal with the time from the light emitting to the light
receiving as a distance signal. Therefore, a light emission trigger
signal from a trigger signal generating portion 48 of a laser
driver 46 attached to the laser oscillator 18 is inputted in the
threshold setting circuit 44, and the fluctuated threshold is
output to the comparator 42. A received light signal is inputted to
the comparator 42, and with the threshold to the corresponding
distance (time) according to the light receiving timing as a
standard, the signal obtained from the photoelectric conversion by
the light receiving circuit 36 is compared to the threshold.
In the comparator 42, by comparing the received reflection light
intensity signal to the threshold, when the received light signal
is smaller than the threshold, the light signal is judged as a
ghost caused by raindrops, and when the received light signal is
greater than the threshold, the light signal is regarded as an
obstacle. When the light signal is detected as an obstacle,
received light trigger is outputted to a time difference measuring
circuit 50 in order to calculate the distance. At the same time
light emission trigger from the above-described trigger signal
generating portion 48 is inputted to the time difference measuring
circuit 50, and the time difference signal of both triggers are
calculated and outputted to an object distance calculating circuit
52, where the distance to the detected object is obtained.
The detected object distance which is obtained, with the signal
from an angle detector 54 detecting a radiation angle by the signal
from the encoder 24, is outputted to a sensor controller 56. The
sensor controller 56 inputs each signal of a vehicle traveling
direction and a vehicle speed from a vehicle controller (not
illustrated) at the same time. By determining whether the detected
object is an obstacle or not from the relationship among the
detected object distance and direction, and the vehicle traveling
direction, when the detected object is judged as an obstacle, an
obstacle signal is outputted to the vehicle controller. In the
vehicle controller, an obstacle signal generating means is
actuated, and various kinds of corresponding measures are conducted
such as the generation of a warning sound as a dangerous signal, a
warning display, automatic halting of the guided vehicle 40, or the
like.
A pair of the laser obstacle detection sensors 10 constructed as in
the above are attached at right and left portions of the front edge
of the automated guided vehicle 40, and radiates a laser beam
oscillated from the laser oscillator 18 from the light projecting
window 14W to the outside through the light projecting mirror 20.
The light projecting mirror 20 is rotated by the motor 22, and
accordingly, the laser beam is continuously radiated over the range
of 360.degree. in a direction of the circumference as the laser
beam is rotating. Since the reflection surface of the light
projecting mirror 20 is set to face higher than the horizontal
surface at this time, the reflection surface is rotated in a
cone-shaped form, so that a ground surface at short distance is
prevented from being detected as an obstacle, even if the vehicle
40 is partially loaded with a heavy load. At this time, if the set
angles in an upward direction of the right and left sensors 10 are
made to be different so that an obstacle detected by only one of
the light received signals of both sensors 10 is excluded, a ground
surface is prevented from being detected as an obstacle.
When a laser beam rotatively radiated is reflected by an obstacle
or the like, this reflection enters through the light receiving
window 16W of the sensor 10 and then enters the light receiving
circuit 36 through the medium of the light receiving mirror 30.
Since the light receiving mirror 30 is connected to the motor 22
and is rotated synchronously with the light projecting mirror 20,
the light receiving mirror 30 can receive the reflected light from
the obstacle at the same position. Since this light receiving
position and the light projecting position are separated up and
down by the driving section casing 12D and the windows 14W and 16W
are not directly connected, a short-cut laser beam is prevented
from being received and the reflection from the raindrops
contacting on the windows 14W and 16W are not received if any
raindrops are contacting on the windows 14W and 16W. In the light
receiving mirror 30, the second mirror 30M for a medium range and
the third mirror 30S for a short range which are curved with a
specified curvature are formed in the central portion of the flat
first mirror 30L. When an obstacle approaches in close proximity to
the vehicle 40, the reflection from the obstacle can enter the
light receiving section as long as the reflection enters through
the light receiving window 16W. Thereby, the detection at short
distances can be achieved and a dead zone can be decreased as much
as possible.
The photoelectric conversion of the reflected light entering
through the light receiving mirror 30 is conducted by the
photoelectric conversion element 38, and the light intensity signal
is inputted to the comparator 42 in the light receiving circuit 36.
The light intensity threshold regarding the distance up to the
reflection object is inputted to the comparator 42 with the light
emission trigger signal as the starting point, and then the
threshold corresponding to the timing at which the received light
signal is inputted is set. When the photoelectric conversion output
signal is greater than this standard threshold, the comparator 42
outputs a light receiving trigger, from which along with the light
emission trigger signal from the trigger signal generating portion
48 in the light projecting section, the time difference from the
light emission to the light receiving is obtained by the time
difference measuring circuit 50 and the distance up to the detected
object is detected in the distance calculating section 52. This
distance signal is not outputted when the received light is the
reflection from raindrops, and even when the received light signal
is at a short distance with high intensity, the received light
signal is blocked by the threshold corresponding to the distance,
so that the distance signal is not outputted as a result of being
judged as a ghost caused by rainfall or snowfall when the light
received signal is less than the threshold. Conversely, when the
distance signal is outputted, the reflected light is recognized as
being from an object with material substance, therefore the sensor
controller 56 outputs an obstacle signal after comparing the
distance signal with the traveling direction of the vehicle, and a
measure can be taken against the obstacle by generating a warning
sound, halting the vehicle 40, or the like.
Though in the above-described embodiment, an example equipped on
the automated guided vehicle 40 is cited, the present invention is
not limited to this example.
As described in the above, by the present invention, the obstacle
detection method uses a sensor detecting the presence or the
absence of an obstacle by radiating a laser beam radiated from a
laser beam source to the outside of the casing through the light
projecting mirror and then by letting the reflected light from an
obstacle or the like enter the light receiving element through the
light receiving mirror. By this, it is determined whether the
reflected light is from raindrops or the like, or not, by comparing
the received light signal output to be inputted to the
above-described light receiving element to the threshold previously
determined based on the correlation between the detected distance
and light intensity. When the obstacle has material substance, the
detected distance up to the obstacle or the like is calculated and
outputted to determine the presence or the absence of the obstacle.
Therefore, the present invention is especially useful to be
equipped on an automated guided vehicle (AGV), and raindrops and so
on are not misdetected as obstacles.
In the sensor detecting the presence or the absence of an obstacle
by radiating a laser beam radiated from a laser beam source to the
outside of the casing through the light projecting mirror and then
by letting the reflected light from an obstacle or the like enter
the light receiving element through the light receiving mirror,
light directly reflected from the above-described light projecting
window is prevented from being received by forming the light
projecting window and light receiving window with a space provided
between them. The light projecting mirror is positioned so as to
face the above-described light projecting window and the light
receiving mirror is positioned so as to face the above-described
light receiving window. Thus, the effects of preventing
misdetection of the raindrops attached to the light projecting and
light receiving windows of the laser beam and of preventing
misdetection of the ground surface as an obstacle are obtained by
enabling synchronized rotation of the light projecting mirror and
light receiving mirror by attaching both of the above-described
mirrors at the rotation shaft of the same motor provided between
both mirrors, by rotating and radiating the light projecting laser
in a cone-shaped form with the optical axis radiated to the outside
of the casing by the medium of the reflection surface of the light
projecting mirror being set in a higher direction than the
horizontal line, and by constructing the light receiving reflection
surface of the light receiving mirror by a combined reflection
surface having the flat reflection portion and the curved
reflection surface with varied curvatures to reflect to the
above-described light receiving element.
* * * * *